Conventional communication systems mostly comprise a backbone part and an access part. For example, a wireless communication network may comprise a Radio Network Access (RAN) part, which establishes and controls the wireless access, and a Core Network (CN), through which other networks and other users of the wireless communication network are connected. Another example of a packet data or a packet switched communication network is the communication network established between the servers and routers of the World Wide Web (WWW). With the steady increases of data demand, interfaces and networks are improved to handle the increased load. For wired connections in the network, optical data transmission using fibers is used to enhance the link capacity between such interfaces.
In communication systems, such as systems using optical data transmission, wireless, wireline or powerline communications, digital data values may be transmitted by means of an optical transmission signal. The optical transmission signal is generated by modulating the phase and/or the amplitude of an optical carrier signal. For example a carrier frequency of the optical signal is changed in dependence on the transmitted data values and in accordance with a constellation diagram of a respective Phase-Shift Keying (PSK) modulation or Quadrature Amplitude Modulation (QAM) method. Prominent examples are Binary Phase Shift Keying (BPSK), Quaternary Phase Shift Keying (QPSK), 16 QAM, 64 QAM, etc.
Moreover, conventional concepts may use polarization multiplexing for data transmission, i.e. different polarization may be used to transmit different transmit symbols simultaneously. Optical fibers are used for transmitting optical signals. Non-linear effects may impose limits on the performance of optical communication systems. In particular, systems using Polarization Division Multiplexing (PDM) can be limited by cross-Polarization Modulation (XPolM). This effect can be predominant when the power of the transmit signal is close to the non-linear threshold, e.g. notably when using PDM-BPSK modulation over existing submarine cables based on Non-Zero Dispersion Shifted Fiber (NZ-DSF). The Signal-to-Noise-Ratio (SNR) and the Q-factor can thus suffer from large variations.